Access to the circulation is essential to provide hemodialysis treatment to people with ESRD. However, vascular access failure is a major cause of morbidity and expense in care of these patients. An established arteriovenous fistula is the recommended access due to longer survival and fewer complications compared to a graft. Unfortunately early fistula thrombosis occurs frequently and many fistulas do not develop adequately to support hemodialysis. If a fistula cannot be established, an arteriovenous graft is used. Although grafts can be used earlier, over half will fail within a year of placement. The cause of graft failure is neointimal hyperplasia leading to stenosis and thrombosis. To address these problems the Dialysis Access Consortium (DAC) designed and initiated two separate trials: one for fistulas and the other for grafts. The fistula trial entitled, "Clopidogrel Prevention of Early AV Fistula Thrombosis," is a randomized double-blind placebo controlled trial to determine if 6-weeks of clopidogrel given at the time of access placement increases the patency rate of newly placed fistulas. A secondary aim is to determine if clopidogrel increases the number of fistulas that are suitable for dialysis. A sample size of 1284 provides 85% power to detect a 30% reduction in the primary endpoint, 6-week fistula patency. The graft trial entitled "Aggrenox Prevention of Access Stenosis," is a randomized double-blind placebo controlled trial to determine if dipyridamole given in the form of Aggrenox (which also contains a small amount of aspirin) can prevent access stenosis and prolong primary unassisted patency in newly constructed grafts. Monthly measurement of access flow rate is done to detect hemodynamically significant stenosis before the graft clots. A sample size of 1056 provides 85% power to detect a 25% reduction in the primary endpoint, primary unassisted patency. Enrollment into both trials began in January 2003 and is scheduled to end in early 2007. Data is collated and analyzed at the Data Coordinating Center at the Cleveland Clinic. An external advisory committee monitors safety and efficacy. The present proposal seeks to continue participation by the University of lowa-affliated Eastern Iowa Western Illinois Vascular Access Consortium in collaboration with the DAC to successfully complete these two important trials. If the treatments are proven to be beneficial, they will substantially reduce the morbidity and possibly the overall cost of providing care to hemodialysis patients.